High octane alkylate is a major blending component of gasoline motor fuel. "Alkylate" generally refers to a mixture of alkanes resulting from the alkylation of C.sub.2 -C.sub.6 olefins (alkenes) with C.sub.4 -C.sub.6 alkanes. It is most desirable that the product mixture, i.e., alkylate, contains predominantly trimethyl pentanes since these are high octane components which add value to gasoline motor fuel. The use of alkylate as a gasoline motor fuel component has become more important owing to government regulations which restrict the use of lead components and butane. In the past, adding lead anti-knock compounds was the easiest way to increase gasoline octane, but because of the deleterious effects of lead emissions, the Environmental Protection Agency (EPA) has mandated the phasing out of the use of lead compounds in gasoline motor fuel. Butane is another effective octane booster, but easily evaporates, especially in warm weather, contributing to smog formation and the resulting atmospheric pollution. The EPA has also required the reduction of butane content of gasoline motor fuel.
The alkylation of olefins by alkanes to give alkylate is a well known reaction and is generally catalyzed by strong acids. Sulfuric acid and liquid hydrofluoric acid (HF) are the commercial catalysts of choice because of their high conversion and selectivity. Of these two catalysts, HF has been favored partly because of the relative ease of HF regeneration.
Recently, hydrofluoric acid (HF) has come under environmental scrutiny owing to its classification as an Acutely Hazardous Material. Furthermore, in southern California the Board of the South Coast Air Quality Management District recently required that the use of HF in alkylation processes be phased out by Jan. 1, 1998. Accordingly, there are incentives for finding substitutes for HF. One such substitute is a solid catalyst which is the reaction product between one or more of the metal halides active as Friedel-Crafts catalysts and a refractory inorganic oxide having surface hydroxyl groups. The refractory inorganic oxide also has dispersed on it a metal having hydrogenation activity for olefins.
One problem associated with solid bed catalysts is that they have limited stability with lifetimes under six hours being common. Attempts at solving this problem have centered on using halides in the feedstream. One such procedure involves using hydrogen halides and/or alkyl halides as the halogen source. However, this results in halogen being present in the product alkylate stream. Accordingly, applicants have developed a solid catalyst alkylation process which effectively removes halides from the product stream in an integrated separation zone and recycles these halides in order to achieve an efficient and economical process.